Lazy Loading Feature Plugin

Description

Lazy Loading Feature Plugin is an official plugin maintained by the WordPress team. It is intended for testing of automatically adding the loading HTML attribute to images and other elements that support it.

To test, install and enable the plugin. It will automatically add loading="lazy" attributes to all images in all new and existing posts, pages, and text widgets on the front-end.

Then use one of the browsers that support it (Chrome, Opera, Firefox, Edge, Android, etc.) and visit the site. Best would be to test over a slower connection, with a phone, etc. and test web pages that have a lot of images, like gallery posts.

Things to look for

Obvious bugs, for example images are missing.

Try to scroll down as soon as the page loads. All images should be at their places, and the page shouldn’t “jump” when images are loaded.

Note to developers

This plugin is intended for testing. If the tests are successful, this functionality will be added to WordPress, but the exact code may change, perhaps significantly.

Reviews

The plugin just adds the loading="lazy" attribute, which works fine, the rest is done by the browsers who support it, which will soon be all relevant ones, since Safari is about to implement this feature. This is a huge improvement for the web platform and web performance in general, I can't even imagine the amount of data (and thus time, energy, CO2, money...) this will save once WP implements it in core.
The lazy loading experience itself is ok - you DO sometimes see images pop up, but that's a price worth paying, and browsers will hopefully improve this by starting the loading at just the right time.

I like that, a LOT. This plugin does nothing more than adding the loading="lazy" tag to images, no dependencies, no extra javascript being loaded. Gives native lazy load in Chrome and Edge, thus improving experience for 63% of my audience, while not hurting the rest... PageSpeed Insights jumped to 100% on both mobile and desktop (yeah, and real life experience is also improved, tested on mediocre 3G connection).
If HTML validation is important to you, proceed with caution. Online validator at w3c dot org, will throw an error since loading="lacy" isn't standadized (yet?).